1. Field of the Invention
The present invention relates to a retrievable hydrostatic testing tool which may be used to pressure test plastic-lined wellbore tubing and the like.
2. Prior Art
It is common practice to pressure test wellbore tubing for leaks as it is run into the wellbore. This involves testing a stand of tubing at a time, as it sits suspended at its upper end by slips seated in the wellhead assembly. In this process, a testing tool is first positioned within the stand. In a broad sense, this tool comprises vertically spaced apart packers, carried by a mandrel, which packers can be expanded against the tubing inner surface, to create a sealed annular space bounded by the tubing, the mandrel, and the packers. The annular space is filled with water introduced through the tool; this water is then pressured up to a high pressure. The pressure is monitored and, if it drops off, a leak is indicated. The still-pressured stand can then be pulled up and the leak visually located.
A prior art hydrostatic testing tool is illustrated in FIG. 1(a). This tool comprises a central mandrel a which may include one or more sucker rods b, to give it length. The mandrel a carries a pair of vertically spaced apart packers c, which may be expanded by fluid pressure applied in the annular space d, to seal against the tubing e. At its lower end, beneath the lowermost packer c, the mandrel a carries a bow spring and slips assembly f. The bow spring and slips assembly f functions, when expanded, to friction-grip the tubing surface to suspend the tool in the tubing. A pressurized fluid inlet assembly h is positioned at the upper end of the mandrel a, above the upper packer c and the wellhead assembly (not shown). This fluid inlet assembly h is designed to be used in conjunction with a pump which supplies water at desired pressure through a conduit i and pessure "gun" or nozzle j. More particularly, the fluid inlet assembly h forms a transverse aperture k for receiving the disengageable nozzle j in sealed relationship. The aperture k communicates with a longitudinal bore 1 extending down through the inlet assembly h. The bore 1 communicates with a longitudinal bore m which extends down through the mandrel a and has an outlet n communicating with the annular space d. A fishing neck o is connected with the upper end of the fluid inlet assembly h, for connection with a cable overshot.
When a first stand of tubing e is to be tested, it is lowered into the wellbore and suspended from the wellhead assembly by slips. The tool, suspended by a cable and overshot attached to the fishing neck o, is lowered into the stand and then pulled up a short distance and set down, to cause the mandrel slips assembly f to expand and grip the tubing wall. This operation is conducted in such a manner that the fluid inlet assembly h ends up protruding above the wellhead. The overshot is released and the nozzle j is inserted into the aperture k of the fluid inlet assembly h. The pump is then started, to fill the annular space d with water and pressure it up. This causes the packers c to expand and seal against the tubing wall. The pressure is then increased to the test pressure (e.g. 5,000 psi) and held there for a short period. If no bleed off in pressure is noted, the stand is judged acceptable. The pressure is then bled off through the conduit i and pump and the nozzle j is removed from the fluid inlet assembly h. A second stand is then added to the first and lowered into the wellbore, with the tool still suspended in the first stand by the slips assembly f. The cable and overshot are subsequently lowered into the second stand, to latch onto the fishing neck o. The cable is then used to pull up on the mandrel a, thereby retracting the slips assembly f, and the testing tool is withdrawn up into the second stand, in preparation for testing it.
Now, in recent years, tubing having an internal plastic lining has achieved wide spread use.
The above described prior art testing tool is not compatible with the lined tubing, as the steel slips assembly f tends to cut the lining. It would therefore be desirable to eliminate the slips assembly from the tool and substitute some other controllable and suitable means for suspending the tool in the tubing.
In U.S. Pat. No. 4,305,277, issued to Ball et al, there is disclosed a hydrostatic testing tool for plastic-lined pipe, wherein a pair of pivoting wings are used to suspend the tool. Other U.S. patents of interest include U.S. Pat. Nos. 4,081,990 (Chatagnier) and 2,981,331 (Arterbury). However, to applicant's knowledge, these tools have not won commercial application.
Applicant set out to design a hydrostatic testing tool which would be suitable for use with plastic-lined tubing. Applicant's earliest prototype tool for testing plastic-lined pipe comprised the previously described tool of FIG. 1, except that the bow spring and slips had been removed. A cable and overshot, previously threaded through the second stand, were attached to the fishing neck and utilized to maintain the tool suspended within the first stand of tubing following its pressure test, while the second stand was attached to the first and both stands were lowered into the wellbore.
The problems attendant with this arrangement were as follows:
the pre-threading of the overshot and cable through each fresh stand, prior to its being added to the tested stand, was a time-consuming operation;
during the addition of each stand, the tool was supported only by the cable, which was vulnerable to shearing; and
the 'wickers' on the cable scarred the lining during the required manipulation of the stand while threading the cable and moving the fresh stand into connection with the tested stand.
It therefore became an objective to provide an assembly which would address these problems, unsolved by applicant's own prototype and other earlier units, with a view to alleviating them. Thus the need existed for an assembly characterized by:
the capability of supporting the tool within the tubing without the use of mechanisms damaging to the pipe lining;
the elimination of using the cable and overshot to support the tool while it was being lowered with the tested stand; and
the development of an assembly which was fast to re-set.